PMC_CONTROL_REG
reg = bus_space_read_4(fdtbus_bs_tag, pmc, PMC_CONTROL_REG);
bus_space_write_4(fdtbus_bs_tag, pmc, PMC_CONTROL_REG, reg | 0x10);
bus_space_read_4(fdtbus_bs_tag, pmc, PMC_CONTROL_REG);